Vehicular communications have long been considered to be an enabler for numerous safety and commercial applications. Many automobile manufacturers are in different stages of integrating communication devices in their vehicles for a variety of purposes including safety, assisted driving, entertainment, and commerce. As an increasing number of vehicles start getting equipped with communication capability, large scale ad hoc networks can be envisioned in the near future. Numerous projects worldwide, e.g. in Europe, in the U.S., and in Japan, involve researching and developing the infrastructure for vehicular communications and automotive telematics. Studies have highlighted that the benefits of setting up vehicular networks significantly outweigh the initial setup costs.
Through a vehicular ad hoc network, it would be possible to forward queries from places without internet connectivity to faraway hot spots at a fraction of the cost of current infrastructure, e.g. 3G based communications. This can be accomplished because of the multi-hop data dissemination capability of vehicular networks, which is one of the major advantages of such networks. Multi-hop dissemination can be used for sending safety and emergency warning messages, exchanging neighborhood information queries, relaying data from the internet, etc. Accordingly, multi-hop data flows in a vehicular network could result from a range of applications.
At the same time, multi-hop data delivery through vehicular networks is complicated because of the high mobility and the partitioned nature of the networks. For example, vehicle mobility can have a significant influence on message delivery latency. The existing methods address the setting under the assumption that the density of vehicles equipped with communication radios is sufficiently high so as to have a significant impact. In reality, owing to the life cycle of automobile manufacturing, high density is unlikely. Further, assumptions about the deployment of roadside units typically serve to mitigate the concern about sparse environments. However, the cost associated with the deployment of roadside units may be prohibitive and in many areas vehicular ad hoc networks might be the only option. Moreover, owing to the time-scale of auto manufacturing, it is expected that the fraction of automobiles on the roads equipped with communication radios will be fairly low to begin with and catch up gradually. Due to the low equipped vehicle density, a store and forward method, where vehicles buffer packets and transmit them when another vehicle is in range, has often been the primary data relaying strategy.
Methods have been proposed for routing strategies in urban networks. For example, packets are forwarded to the intersections as quickly as possible. At the intersection, the packets use a geographical forwarding or a right hand rule. There is no consideration of other parameters, such as vehicle density, vehicle speeds, etc., in these strategies.
However, because of the unpredictable nature of vehicular networks, any data dissemination strategy needs to take into account a diverse range of environmental parameters such as vehicle speeds, direction, density radio range, roadway lengths etc. As a result of the high variability of the parameters, it is difficult for heuristic based forwarding methods to function well under the entire range of network conditions.